This invention relates to a light box and to means for providing substantially uniform illumination of a selected work area for use ingraphic arts.
Prior proposed light boxes or illuminated work areas have included different forms of construction in the arrangement of the light source, the interior of the light box, and the top plate-like member providing the backlighted working area. In such prior proposed light box constructions, light sources have included incadescent lamps and fluorescent tubes. Incandescent lamps generated substantial heat which often required cooling means so that the work surface would not become too hot. Prior incandescent lamps were essentially point light sources and uniformity of illumination of the work surface was difficult to achieve. Fluorescent tubes were cooler and did not require the cooling means of the incandescent light sources, but provided an elongated light source in which the intensity of light emanating along the length of the fluorescent tube was nonuniform. In prior proposed light box constructions using fluorescent tubes, various reflective means were used to modify and redistribute the light emanating from the tubes, such modifying means being usually in the form of irregular configurations of the reflective surfaces of the interior walls of the light box, by the use of various forms of baffles supported from the light box, and the use of slits or regulated openings in baffles to redistribute the light.
It is believed that the intensity of illumination in footcandles of such a working illuminated surface area is preferably in the range of between 300 to 400 footcandles. Within this range of illumination, it is desired that the difference in intensity of illumination throughout incremental areas of the working surface be minimized as much as possible so that, for example, the intensity of illumination over the enire working surface may vary, for example, from 350 footcandles plus or minus 15 footcandles. It is also recognized that the extreme marginal or peripheral areas of the working surface may be illuminated with slightly less intensity of light without being objectionable to the user of the light box because most of the work is performed in the remaining work area.
Some prior proposed light box constructions in current use have been measured for uniformity of illumination. Over the working area, variation of intensity of illumination was found to be in the order of 50 to 70 footcandles and in one construction the contour or shape of the lines of the same light intensity were found to be unsymmetrical and light intensity was in a range of from 150 footcandles near the periphery to 270 footcandles adjacent the center of the working area.